Posted
by
samzenpus
on Friday January 04, 2013 @06:20AM
from the stop-moving dept.

First time accepted submitter mromanuk writes in with a story about scientists at Ludwig Maximilian University of Munich who have created an atomic gas that goes below absolute zero. "It may sound less likely than hell freezing over, but physicists have created an atomic gas with a sub-absolute-zero temperature for the first time. Their technique opens the door to generating negative-Kelvin materials and new quantum devices, and it could even help to solve a cosmological mystery."

Epic fail. Every Jedi knight builds his own light sabre. What the galaxy is coming to now a days, aspiring jedi knights nonchalantly ordering their light sabre by mail order... What next? Subject verb object order Yoda learns?

Next is a pre-school class with Yoda with a bunch of 5 years kids. Also the kids get the light sabres from the dead Jedi, it's all in the brochure: So You Want Your Kid To Be A Jedi. Oh yeah, your kid need to take drugs if they get to puberty, because love is forbidden and leads to the dark side.

If I were patient enough, I could probably produce a series-produced automobile from junk parts. Especially if I worked in a junkyard.

Of course, a car yard is more likely to see junked 1968 Fords come through than any desert backwater world is likely to see lots of wrecked C3-series Protocol Droids... except that (as pointed out elsewhere) Jabba seemed to go through protocol droids at a fair clip.

There cannot be any proof, it is obviously impossible to distinguish between "simulated" and "real" reality

Not that obvious to me. You're assuming the simulators have made a perfect simulation, which they may not have done. Or they could leave deliberate clues, if they so wished, which would help us distinguish simulation and reality. Of course, on a broader philisophical point, you could argue there would still be no difference - reality could be a simulation and still be real.

Hi there,You can stop philosophizing, I just deleted that guy from the simulation, he was getting annoying. Incidentally, if you subscribe to the specific flavor of mass delusion you guys call 'Christianity' and are wondering when the rapture will happen, it'll come the day I finally slip up while combining wild-cards and the 'rm' command on my Simulatron 6000 (TM).

There cannot be any proof, it is obviously impossible to distinguish between "simulated" and "real" reality

Not that obvious to me. You're assuming the simulators have made a perfect simulation, which they may not have done. Or they could leave deliberate clues, if they so wished, which would help us distinguish simulation and reality....

Why do you assume reality is "perfect"? Perhaps inconsistent results is part of the built-in quantum randomness of the Universe.

Put lots of little magnets in a magnetic field. They will line up with the field. At absolute zero there will be no (technically minimal[1]) deviation from them all being perfectly aligned. As you warm them up they will start to be less and less well aligned until at what we call infinite temperature, there is no alignment with the field at all and the alignment is completely random.

But, if instead of warming them up, you flip the magnetic field they will then "cool" through "infinite" temperature.

If we use this definition of temperature then it would make more sense to have absolute zero as negative infinite temperature, infinite as zero and still hotter temperatures as greater than zero.

This makes the unreachability of absolute zero make more sense. "Infinite" temperatures (and greater than infinite) are only unreachable via trying to add more heat.

Lasers utilize population inversion - which is a state that is impossible via naive thermodynamics and also does not have a sensible temperature as a result.

Actually, since this is predominantly a computer science crowd, let's try to explain it in purely binary terms (or a simplified pure quantum mechanical model if you wish). Every particle in your system is a binary bit; 0 is ground state (low energy) and 1 is excited state (high energy). Now, our kelvin scale is defined so that 0K is all 0s (there's only one state that satisfies this criterion) and +infinity is a 50/50 mix of 0s and 1s (which has the largest number of possible combinations/states:= highest entropy). That worked pretty well for a long time since one never can go higher than 50/50 through ordinary heating. The problems started when people figured out clever tricks to have more 1s than 0s. This is called a population inversion, and LASER and NMR/MRI rely on it. The temperature of such an inverted population would be "beyond infinity", in other words, not representable in the kelvin scale. The solution was to use negative temperatures for these inverted populations: all 1s would be -0K (the fact that -0 is not the same as +0 is not a problem because neither of these states can ever be reached), and the temperature would go down (-1, -2,...) as 0s are introduced, to ultimately reach -infinity at the same 50/50 mix as +infinity (so basically + and - infinity are the same state). This weird system turns out to have mathematically convenient properties. Just to get an idea, if one inverts this temperature scale (ie. define a new new (K^-1) scale that goes with 1/T), the 50/50 state would be 0(K^-1), all 1s is -infinity (K^-1) and all 0s is +infinity (K^-1), so the problems at 0 and infinity are solved.

Remarks: - given the above, I feel it's more correct to state that inverting a population is going through infinity [wikipedia.org] (as opposed to going through zero).
- inverted populations are not stable; when perturbed, they always equilibrate to positive temperature states (and they cannot be maintained through ordinary heating as another reply incorrectly stated, though they can through pumping, as in continuous-wave lasers [wikipedia.org]). This equilibration can, however, take several seconds (in NMR applications) - long enough for practically useful applications.

TL:DR; version: negative temperature matter doesn't contain less energy than 0K; a good deal more in fact.

It seems this is a very specific quantum mechanical perversion, and no classical systems can reach the state quantum physicists call "negative temperature".

This is by no means a quantum perversion, just a natural consequence of the definition of temperature as 1/T = dS/dE. There's nothing mysterious about negative temperatures from a thermodynamical point of view, it just happens that calssical systems don't exhibit this property because they do not come with an upper limit on energy, whereas there are quantum ones that do.

The common interpretation of temperature as average energy per degree of freedom comes in via the equipartition theorem, but breaks down in various edge cases, eg when the energy levels cannot be approximated by continuity (eg heat capacity of diatomic gases) or for non-ergodic systems (some plasmas, I believe).

As to the problem of infinite temperature: In a sense, thermodynamic \beta = 1/kT is the more natural measure of hotness and coldness and has a pole at T = 0. Coming from T > 0, this corresponds to infinite coldness, whereas coming from T < 0, this corresponds to infinite hotness.

How about you instead explain in normal people terms (or at least computer specialist terms) how atoms can have less motion than not moving at all, because that sounds completely made up and impossible.

It's actually not quantum mechanical, at least not explicitly, but it requires that the system in question have an ordered state that is at a high-energy bound.

A classical system that does this is an array of magnetic dipoles in a magnetic field. When all the dipoles are aligned against the field, the system is fully ordered, and is in its highest-energy state. If you look at deviations from this state, what you find is that all of them increase the entropy (because the state is fully ordered), and decrease

While I think he gave himself an out in the specification/qualification of 'first year student', there's a degree of hypocrisy in that vs. this [youtube.com]. (Specifically after the 4 minute mark where he basically says you can't properly explain certain things in physics through intuitive metaphors.)

While I think he gave himself an out in the specification/qualification of 'first year student', there's a degree of hypocrisy in that vs. this [youtube.com]. (Specifically after the 4 minute mark where he basically says you can't properly explain certain things in physics through intuitive metaphors.)

I don't think there is hypocrisy. I think "explain something to a first year student" implies the student is taking a course in physics, i.e. probably 3 hours of lecture per week times 30 weeks, plus a lot of individual study time. What he is saying in the video is that he can't explain magnetic repulsion to a non-student in a 7 minute video. I don't think that is a contradiction. By the way, Feynman taught the freshman physics class taken by everyone (i.e. mostly non-physics majors) at CalTech, so take it

Temperature isn't defined in physics as anything to do with heat, but the derivative of energy with respect to entropy. Absolute zero is the temperature at which there is no energy left in the system. At normal temperatures, it is positive. At absolute zero, it's zero. If you can create a system with dU/dS as negative, it's technically negative temperature, even though the system still has energy.It's hard to explain due to how things like temperature and energy are defined, not because physicists are being smug. There isn't a proper name for it because it doesn't happen very much. That's why it's news.

Temperature isn't a property of individual atoms. It is a property of a huge set of atoms, describing their energy distribution.

In a body with positive temperature, there are more atoms in the low energy states (moving slowly) than in the high energy states.

In a body with negative temperature, there are more atoms in the high energy states than in the low energy states. Normally that can only happen if there is an upper bound to the energy. Kinda like a speed limit, or, more realistically, if the states being talked about are not related to speed at all, but to some other physical property of the atom (such as orientation of spin within an external magnetic field...)

You explanation is informative. Not only is your definition of temperature new to me, I find the consequences unfortunate. They should have a different term for this state rather than "negative temperature". Sure it's interesting physics, but the headline seems a bit sensational due to the definition of temperature needed to make it possible.

Temperature isn't defined in physics as anything to do with heat, but the derivative of energy with respect to entropy. Absolute zero is the temperature at which there is no energy left in the system.

That's slightly inaccurate. Absolute zero actually occurs when each particle has one and only one energy state available to it. There's still energy; just not enough to excite a particle or transfer from one to another (since each particle can't give up any energy).

If by "retarded," you mean "correct," then yes, that explination is very "retarded." If you bothered reading the wikipedia article, it explains it pretty clearly:"The paradox is resolved by understanding temperature through its more rigorous definition as the tradeoff between energy and entropy, with the reciprocal of the temperature, thermodynamic beta, as the more fundamental quantity.""The inverse temperature = 1/kT (where k is Boltzmann's constant) scale runs continuously from low energy to high as +,

Surely it's more important that technical terminology be technically correct than intuitively graspable? There's a reason that computer techs don't refer to the whole computer as the "hard drive", even though that's obviously exactly where you put all your files when they're on the computer.

Not a very good example. A large percentage of lay people refer to the whole case as 'the hard drive'. Techs, depending on their age, are more likely to call it a 'cpu' or 'micro'. Is either term inherently less intuitive or more technical? They both follow the same naming strategy but from a different point of view,i.e., the focus of importance has shifted. Technically, is it really a computer if the first computers were humans?

The big loser for your point is that in reality, terminology for the mos

I'm a techie and I tend to use the terms "box", "machine", or "computer". CPU is technically wrong also, since that refers to the main processor (excluding motherboard, RAM, hard drive, and everything else), but some techies still use it. I can't recall anyone calling it "micro". My wife still calls it a hard drive, no matter how hard I try to teach her otherwise.

Not a very good example. A large percentage of lay people refer to the whole case as 'the hard drive'. Techs, depending on their age, are more likely to call it a 'cpu' or 'micro'. Is either term inherently less intuitive or more technical? They both follow the same naming strategy but from a different point of view,i.e., the focus of importance has shifted. Technically, is it really a computer if the first computers were humans?

It seems to me to be a retarded description, like calling infinity + 1 a negative number.

They need to use a proper name for it, not something that only makes sense if your the kind of person that likes to say things in such a way that no one else understands what you mean just so you can claim its technically correct with a smug attitude.

Just means the computers the Matrix is running on happen to use signed values.

It's all a trick due to the weirdness of quantum states trying to be defined in classical terms

They change the quantum state of atoms with almost no energy, to a higher energy state and keep them there using less energy than the change in state... so in classical terms the energy had to come from somewhere and so the average temperature must have gone down.... but the missing energy is not really missing and the real temperature is still positive...

This is one of the things I love about slashdot. People with no knowledge of a subject call professionals "retarded" and get modded insightful.

It seems to me to be a retarded description, like calling infinity + 1 a negative number.

Think about reciprocals.

They need to use a proper name for it,

How about "nagative temperature". That's a proper name for it.

Temperature is defined by energy and entropy. Add energy and the entropy increases. That means the temperature is positive. How positive is how big that change is. Nice, straightforward, works well. Does whay you expect.

Then some quantum physicists discovered that adding energy makes the entropy go down. Well, plug that into the definition of temperature and the number comes out negative.

So basically, what you are claiming is that physicists are retarded because you don't like how the maths work out and you would rather they change the perfectly good classical definition of temperature to fit your sensibilities.

Deal with it. Quantum physics is very strange and many ideas you bring with you from the classical world simply don't work.

Hot heads, operating at positive temperatures, are just bouncing around ignorantly smashing into people with their stupid comments and increasing the noise to signal ratio, and causing others to get all hot and bothered as well.

I don't know, the classical and the quantum seem to be quite harmonious here....you just have to deal with the fact that with a 'cool head' of logic you also qualify for t

Having negative temperatures be "higher" than positive ones actually makes a lot of thermodynamic sense. For one thing, it lets you preserve the notion that heat naturally flows from hotter things to colder things.

Formally speaking, it's more natural to think in terms of the inverse of temperature, 1/T, sometimes called beta. In the limit of very large positive beta, that's nearly absolute zero, and is the low-energy end of the spectrum. A beta of zero is full disorder. Negative beta corresponds to high e

it's perfectly obvious (after a few minutes' pondering of course) to anyone who has taken a decent stat mech course. and if you haven't, it's perfectly obvious after giving it an hour's pondering. seriously, the wikipedia page is very good.

but, only since i can't help myself, i'll try and break the wikipedia page down even further. in short, temperature is the inverse of the rate at which entropy increases as kinetic energy is added to a system of particles. the hotter a classical system gets, the less effe

While the absence of punctuation is condemnable (and you're guilty of it too), that sentence doesn't qualify as a run-on, since it doesn't contain two independant clauses, but one main clause and a chain of subordinate clauses.<\pedantrysquared>.

Observtions during the experiment could point to new research on dark energy.

From TFA:

Another peculiarity of the sub-absolute-zero gas is that it mimics 'dark energy', the mysterious force that pushes the Universe to expand at an ever-faster rate against the inward pull of gravity. Schneider notes that the attractive atoms in the gas produced by the team also want to collapse inwards, but do not because the negative absolute temperature stabilises them. “It’s interesting that this weird feature pops up in the Universe and also in the lab,” he says. “This may be something that cosmologists should look at more closely.”

Could we even answer that question without an absolute reference frame in an infinite universe with gravitational attractions from just about everywhere?

And you go on like this, but the universe is expanding and accelerating away from us in all directions and there is no absolute reference frame, yet GR works just fine. Dark energy is responsible for this and was put into the equation as the cosmological constant by Einstein himself, although he removed it and it wasn't put back in until dark energy was discovered in the 90s.

HAH! When I was a freshman in college a long long time ago, I lost points in a computer science assignment because I did not perform error checking to ensure the user enter temperatures were above absolute 0. Prof didn't believe me when I told her that wasn't a hard limit, so there!

And your prof was right - the user can still be stupid and you, as a programmer in this instance, should have worked to ensure that the user COULDN'T do anything bad by being (deliberately or not) stupid.

Take, for instance, things like this were a result from an experiment erroneously kicks out -0.000001 K and you allow it into your program to wreak havoc with your assumption (e.g. if you were storing it in unsigned at any point, or dividing by it assuming it was always >0 K).

But in the news story it says SUB and SUB means below, yet there is no mention of the temperature whatsoever in the article and going beyond absolute zero is not possible even out in space! You can get close, but not to absolute zero otherwise you would have created the ultimate weapon!

Sometimes you take an idea with a perfectly normal, intuitive meaning - "temperature is a measure of how fast the atoms are going" - and formalise it. In this case that formalism is something along the lines of "temperature is a measure of the population distribution of the kinetic energy of the particles in an ensemble". Well, sometimes when you make a definition like that, and you invent something that doesn't exist in nature - a laser, say - then you try to apply that definition to the new object, and yo

Kelvin temperature is a reflection of average thermal energy per unit volume. Most matter still behaves a certain (normal) way and while there are a few high-energy particles, a majority of the particles in it possess an "average" amount of energy. For some materials, evidently, the particles' energy properties are inverse in this respect and have more than an average number of high energy particles. The lowest temperature that you cou

Proving/Disproving God isn't a Scientific Mission. Understanding how the Universe works is.If we ever figure it all out we can go.Well that is how the Universe Works and that is it.or we can go.Wow so that is how God did it.

You are confusing the Idea of a God with Religious interpretations of God. Science has more or less disproven that the Stories in the Bible are often not Factual or at least exaggerations. But it doesn't disprove God.

God and Science do not Mix. The God idea exists outside of Science as God is defined as a SuperNatural entity or more plainly God exists out of the rules of Observable Nature, Science is the study of Observing Nature.This come with a two edge sword.

1. Any Science that states that God did it, is faulty because God is unobservable thus you cannot equate it as an observed fact. At best if there is a God Influence it would probably be considered a seemingly Random Element that will need further study.

2. The counter to this, is Science can't disprove God, because he is out of Observable Ability. Thus any work to Disprove God will be trying to apply God as a factor to disprove it.

Your problem is that you are using a naive layperson perspective for your definition of God, equally grievous as using a naive religious description.

What if 'God' is simply the sum total of everything. Are we not created in his image? We, as 'individual' humans are composed of hundreds of different systems, with different purposes, all somehow working together as a functioning whole.

God, put simply, is the set of all sets. Absolutely no problem in science studying that.

Bleah your post has several glaring deficiencies:1) your definition of God as "unobservable" is only one of the many different (and quite often incompatible) definitions of God.Science can (and did) rule out many definitions of God (where God should have been observed but wasn't) so for these Gods, science is atheistic.

2) if you start from a definition of God as unobservable, then what you know about this God was necessarily reached only but a pure construction of human minds, an hypothesis in other word.So